Lapel microphone



June 29, 1937. R. w. CARLISLE LAPEL MICROPHONE Filfid April 30, 1954 2 Sheets-Sheet l INVENTOR RICHARD M CARL/6L5 BY ll M ATTORNEY June 29, 1937. R. w. CARLISLE LAPEL MICROPHONE Filed April 30, 1934 2 Sheets-Sheet 2 \MENQQNV swadsyy 5 39% kEMQXuQN Jswads y t a u R E 0M m T ma m V A c m Patented June 29, 1937 f UNITED .STATES LAPEL MICROPHONE Richard W. Carlisle, Haddonfield,

N. J assignor to Radio Corporation of America, a corporation of Delaware Application April 30,

2 Claims.

The present invention relates to microphones, and more particularly to the variety thereof adapted to be worn on the person of a performe in order to pick up his voice.

1 Microphones of the aforesaid general type have been previously made, but theyhave had undesirable characteristics both as to inherent noise and as to frequency response, and, particularly as to frequency response from the voice of the performer.

I I therefore propose to provide a microphone of the ribbon or fvelocity type which is peculiarly adapted to be worn upon the coat lapel of, or in an equivalent position upon the body of, the

performer, and which provides uniform characteristics both as to frequency and as to volume,

irrespective of the relative position of the performers head.

One object of my invention is to provide such a microphone which will irrespective of the position of the performers head in relation to it.

Another object of my invention is to provide such a microphone which will provide a normal frequency response irrespective of the usual direc;

tional frequency characteristics of a performers voice.

Another object of my invention is to provide an' improved microphone of the magneto-generative ribbon, or velocity.type, as distinguished from the pressure-operated resistive or capacitative types of microphones.

Other and ancillary objects of my invention will hereinafter appear to those skilled in the art 1 from a study of the accompanying drawings and a reading of the following specification.

In the drawings: I

Fig. 1 is a view of my improved microphone in completely assembled form.

Fig. 2 is a dis-assembled view of the microphone.

Fig. 3 is a diagrammatic illustration of the mounting of my microphone on the coat lapel of a performer.

Fig. 4a is a diagrammatic illustration of the frequency response characteristics of my microphone in one direction.

Fig. 4b is a. diagrammatic illustration of the frequency response characteristics of my micro- 50 phone in a second direction.

Fig. 4c is a diagrammatic illustration of the frequency response characteristics of my microphone in a third direction.

Fig. 5a is a diagrammatic illustration of the volume response characteristics of my microphone in the most remote position of the performer's mouth.

Fig. 5b is a diagrammatic illustration of the volume response characteristics of my microphone in the average position of the performers mouth.

provide a uniform volume 1934, Serial No. 723,230

Fig. 5c is a diagrammatic illustration of the volume response characteristics of my microphone in the nearest position 01 the performer's mouth.

Referring now to the drawings:

In Fig. 1, I 0 represents generally my microphone in assembled form, I I is the transformer therefor,.and I2 is the connecting cordwhich permits the transformer II .to repose in a convenient pocket of the performerwwhenjthe microphone I0 is retained upon his coat lapel by the phosphorbronze clip I 3.

As shown in Fig. 2, the elements of my microphone proper comprise an electro-magnetic unit generally indicated at I4, and hereinafter described in greater detail, a rectangular casing I5 carrying 'the clip l3, and a plurality of endplates I6 and I! which, held toward each other by the screw I 8, secure the assembly together.

The screw I8 passes through the hole I9 in one end-plate and is received in the nut 20 secured to the other end-plate. It is, of course, immaterial, which end-plate carries the hole and which the nut so long as the head of the screw I8 substantially counterbalances the nut 20..

Between the ends of the unit l4 and each of the end-plates is interposed a felt washer 2| (only one of which is shown) permitting a firm clamping of the unit I 4 by the end-plates with sufficient rigidity and yet with sufliciently damped elasticity to permit the unit I 4 to be retained firmly and yet non-resonantly in positive but unrigid spaced relationship with the casing I5, I6 and I1. Such construction prevents the transmission of extraneous mechanical noises, such as those due to rubbing of clothes, etc. to the microphone.

To refer now more generally to the construction and purposes of applicant's device:

The principal purpose of using a lapel microphone as contrasted to a stationary microphone in front of a speaker is to permit the speaker to move freely around a studio, stage or lecture platform or turn away from the audience without there being any appreciable change inthe intensity or quality of his voice, as heard by the audience, due to the variation in distance and azimuth with respect to the microphone. This reduces the amount of monitoring to a minimum. There is also some advantage to be gained in the fact that it is not necessary in the lapel microphone case to obstruct the audience's view of the speaker. I

In ordinary public address, sound re-enforcing, news reel pickup and for many broadcasting purposes, convenience in microphone placement is an important factor.

With the lapel microupon the grid of a vacuum tube to the pressure in; relatively independent of free free space shall-be quency.

It is well known that the quality of the human" voice changes as the speakers head is turned relative to the auditor. In the case of the ordinary microphone, we neglect to compensate for this effect because we reallytransplant the auditors hearing mechanism to the position occupied by the microphone and any frequency discrimination merely adds to the naturalness of the action. I Inv the case of I the lapel microphone we are primarily interested in obtaining maximum artic'ulation. The articulation depends essentially upon the shape of the acteristic, the width andthe location in the frequency spectrum of the transmission band. The

was extended by Stewart who ap lied" it over a sound around the human head.

For this particular-analysis we will assume, following the analysis by Stewart, that a small source (at 9=0) located on the surface of a sphere 7.5 inches in diameter represents the human voice. The approximate angular position of the lapel microphone is where 9=90. I 'I I The ratio .of the pressure at 9:0 to' that where 9:90 was calculated assuming a plane wave impinging on thebottom of the sphere. Measurements were made of a small source of sound at various distances from a condenser microphone, which indicated that little change in frequency characteristic occurred as the source was 'moved from a large distance up to the vic;n-, ity of the microphone. I I I Two types of microphones may be used for this particular purpose, namely one whose response corresponds to the pressure in the sound wave, or one whose response is proportional to the particle velocity. Each type has certain inherent advantages and disadvantages for this applica I 'tion.

microphone is that when a speaker turns his head towards the side away from the microphone,

there is a serious loss in intensity of the soundv consisting of a thin aluminum ribbon freely suspended in a magnetic field, have been described previously in H. F. Olson-Journal of the Soc. of Motion Picture Engrsvol. 6, page 695 (19311),

Journal of theYAcoustical Soc. of Amer. vol. '3,

page 56 (1931) andProceedings of the I. R.. E., vol. 21, page 655 (1933). These may be summarized by stating that the differential pressure on the ribbon, resulting from the impact of a,

sound wave, is proportional to the mean distance between the front and rear surfaces, and proportional to frequency." The velocity of the ribbon (and hence the induced voltage) is proportional to this pressure and inversely proportional tothe mechanical impedance of the ribbon. The latter frequency response chardiffractionof a plane sound wave around I a spherical obstacle was firstinvestigated mathee matically by Rayleigh; The theoreticalanalysis I microphone.

One of the problems encounteredwith 'a lapel 1 is due to the ribbon mass and the air load, and is proportional to frequency. The ratio of ribbon velocity 2100 2 pressure rt It was, also shown that the sensitivity is a maximum normal to the ribbon, and decreases off the axis-to zero in the plane of the ribbon;

Suppose such a device is placed on thefleft point occupied by his mouth when his head is turned away fromthe microphone. 'Ihenas the speaker turns his-head towards or away from the microphone, the azimuth of his mouth 'varies from a region of low sensitivity to that of maximum sensitivity. The directional characteristic is shown in Figs. 5a, b and a, and the ratio of the directional factor to the distance of separa-' tionmay be seen to be nearly the same for three is a fundamental advantage of the velocity lapel Since the directions of minimum pickup are over the speakers left shoulder or to his lower right side, loudspeakers may be'placed there 1 with optimum immunity from feedback.

The ideal frequency characteristic of a pressure-operated lapel microphone would be the in- 'idealcharacteristic would rise steadily towards the higher frequencies. When used in' a sound -re-enforcing system, this would increase the probability of pickup from the loudspeakers at the frequencies of accentuated sensitivity, with a consequent likelihood of howling. A definite limitation of 12 db. maximum rise with no sharp peaks, using the frequency range of 80 to 7000 cycles, hasgiven very good results. I The microphone consists of a small U-shaped permanent magnet 25 with an extremely thin aluminum ribbon 26 mounted between its poles.

. This ribbon is one inch long, one thirty-second commercial design by appropriate proportioning of the transformer winding inductances, leakage reactance and distributed capacitance. v

The microphone is shown, in assembled and, exploded views, in Figs. 1 and 2. The total weight of the microphoneis three ounces. Itis approximately 1%; inches square and 1 inch thick. A short lead extends from the microphone to the transformer, which may be placed in a side pocket. The microphone parts are enclosed in a perforated metal case lined with silk, with the ribbon on an angle of 45 to the horizontal. A clip on the back of the case is such 2,085,184 designed to fit a lapel buttonhole as hereinbefore proximity to' the instrument. It may also bev clamped on the instrument, utilizing the directivity characteristics ofthe microphone to come 'pensate for the directivity of the instrument.

The foregoing portion of this specification has dealt primarily with matters of volume response, and the relation of frequency response thereto will next be considered, with proper consideration of volume response in relation thereto:

It is quite well known that the quality of the human voice changes as the speaker's head is turned relative to the auditor. In the case of ordinary microphone pickup, we can neglect this because we really transplant the auditors hearing mechanism to the position occupied by the microphone and any frequency-discriminationmerely adds to'the naturalness of the action.

A lapel microphone must accentuate high fre-,

quency as compared to the low frequency response in order to compensate for the diffraction of the voice around the head. There is less high frequency in the vicinity of there is low frequency. Since' the high-frequency end of the characteristic must be the most sensitive. it should not have sharp peaks at which excessive pickup from the loudspeakers (in public address systems) would occur, causing howling. smoothness of high-frequency response is an inherent characteristic of the ribbon type of microphone and the difficulties of diaphragm and other mechanical resonances are obviated. The ribbon principle is therefore utilized in this design.

phone: velocity actuated or pressure actuated. A velocity actuated lapel microphone consists of a thin aluminum ribbon free to'. vibrate with the air current, suspended in a magnetic field. This may be made away from the microphone; then when he turned his head towards the microphone he turned it towards the region of less response. With this arrangement the advantage of the pressure microphoneover the velocity microphone is so small as to be overbalanced by factors of transformer weight and the additional'cost of the labyrinth. It so happens that the velocity ribbon accentuates low frequencies for a source near it as in this case. This permits of a' transformer to be used which cuts off low frequencies and is therefore a lighter transformer than can be used with the pressure microphone, and this is so small that it may be-placed in the same case as the micro phone, y

In Figs. 5a, b, and c are demonstrated the application of the directionaldiagrams of the velocity lapel microphone to maintain constant output as the speaker's mouth is turned from side to side. As mentioned above, the most sensitive pickup region is towards his mouth only when he turns it away from the microphone.

a lapel than There are two ways of making a ribbon micro apt to get through the The relative sensitivity in any position is the ratio of the sensitivity shownby the directional pattern to the distance of the mouth from the microphone. It may be seen that the values for left and right vary only 5% from the sensitivity at the central position. It will vary slightly for diiferent persons. For these reasons locity microphone.

we'have adopted the ve- Due to the building up of low frequencies by a velocity microphone when used near a sound source, frequency compensation inaddition to that discussed previously must be provided at the low frequencies. A velocity microphone located at. a distance 1' inches from the source will accentuate a low frequency f in theratio H velocity 2100 2 pressure rf +1 Thus we have for a distance of rf=9 inches from the source,

f=460, R=1.1 f=230, R=L4 f=115, R'= 2.24 f: 57, R=4.12

So when considerably smaller and lighter magnet is used than in the case of the standard velocity microphone. a narrower air gap than the standard and clearances between thesides of 'the ribbon and the pole pieces are smaller than in the standard. These clearances may be made small because in the case of a lapelmicrophone we do not require as much low-frequency sensitivity as in the case of the standard type and, therefore, a higher natural frequency may be adopted for the ribbon. The tighter the ribbon is stretched,

the narrower the clearances may be made. Standard velocity microphones have a very loose ribbon tuned to approximately 15 cycles per second and therefore must have a greater gap than the lapel microphone in which the ribbon ispreferably tuned between 50 and 100 cycles. The gap is, in the latter instance, determined by four factors: first, the probable sag of the ribbon; second, the minimum spacing to which it can be set in commercial manufacture; third, the diameter of the magnetic saturation.

The magnet conformation shown in the drawings is adopted as giving the minimum leakage for any design which would satisfy the space requirements.

The most desirable magnet length, as at present known, is inch.

It has been shown that in the standard velocity V microphone the difference in pressure between the two sides (which corresponds to the force actuating the ribbin) is proportional to the ire- I'his magnet has largest particles of dirt which are silk screen; and fourth,

The' ribbon dimensions the frequency.

incident sound with respect to the normal to the 1 faceof .the ribbon. The magnet structure en-. closingthe back constitutes essentially'an open pipe, To determine the magnitude and phase at so p of the human voice for 9:90".

A- magnethlonger than the one referred to The pressure available for actuating the ribbon in the lapel microphone in which the per manent magnet encloses the back is not a'simple function of the frequency and the angle of the the points 91, 122 etc. .(Fig. 4a) on the back of the 5 ribbon, we must analyze the structure as an open pipe. At the resonance frequency ofthe chamber 7 30 the pressure at the point X1 isa maximum and the velocity at X2 is a maximum. Besides resulting in tha largest'pressure on-the back side. when resonance obtains, the' difference in pressure between the two sides is largest dueto the fact that the difference in phase is the value which results in the largest difference in pressure.

- The response characteristic will then show a I rise in the characteristic, after which the response will decrease rapidly with frequency. This is, of course, a desirablecharacteristic in view of the necessity of having a rising response characteristic to compensate for the characteristics above causesthe peak to occur at a frequency lower in proportion to the magnet length, thus. reducing the range. Y

In the conventional type of ribbon microphone, the response is zero for sounds originating in theplane of the ribbon. However, due to the magnet structure enclosing the back of the magnet, the response at the higher frequencies is vnot zero for all azimuths of sound originating in the plane of the ribbon. The'magnet structure as pointed out above approximates an "open pipe. The phase shift in' this cavity differs from when sound originates as shown in Fig. 4b.

I Of course; at' low frequencies, the phase difference is very small. -As the resonance frequencyof the cavity is approached, the phase rapidly. The cavity is excited by, resonance because the ,same pressure andphase of the incident souiid exist on the two ends of thecavity.

havepractically zero response because the speed of' propagation in the cavity and in'the open is.

the same. Therefore, the difference in pressure between the two sides of the ribbon is zero. Thisexplains 'in a general way the behavior of the microphone in a sound field.

It is necessary to associate a transformer.

with the microphone. The transformer may eitherbeplaced in the case with the micro- [Zto the microphone and placed in a side pocket. A transformer has been made small and light enough to 'go inside the microphone case.

end (4000-6000 cycles); Below this, the level is made high over the region 2000-4000 cycles bythe transformerrise due to the interaction .of the distributed capacitance of the transthe phase shift along the outside of the ribbon 1400'g. with an air gap of .088".

difference increases rapidly, and, as a conse-' quence, the difference in pressure increases Whenesound originates, as shown in Fig. 40, we

phone element or be connected by a short cord There is a slight acoustic rise at the high former with its leakage inductance. Low frequencies are then tapered off, starting at 1000 cycles. The entire frequency characteristic is thereby sloped.

The transformer is designed to give a greater step-up ratio than a usual, transformer. 'This is justified by the fact that the range is limited to 7000 cycles, and also that low frequencies are Transformer winding data Primary .oseld am. Cu. enamel 12 turns. 'Re

sistance .019 ohms.

Secondary .006 diam. Cu. enamel 510 turns;

Resistance 23 ohms. Bring out primary conductor terminals.

Open-circuit secondary inductance at 1000' cycles,- .18 henry. Coil length 1%. Inside. size X A;

Out side 11% x plus leads.

in sleeve for One of the factors determining clearance tween ribbon and pole pieces was the maximum size of dust particles that could get in. Experiments withscreens of balloon cloth and other fabrics of closer mesh than thesilk used in screening the production ribbon speakers have broughtout no substitute for this silk which Experience with the magnetic circuit indicates that a greater ribbon length is chosen not only does the microphone become more bulky but nothing is to'be gainedfor a given weight of magnet. Unless stricter space requirements are to be placed on the microphone,

there is no pointgin making the ribbon shorter.

'A ribbon'thickness of .0001" is preferred.

Having now described my invention, I claim: 1. In combination with a microphone having its maximum response in a single direction,

means for supporting said microphone upon the person of a speaker in such position that the direction of maximum response is in the direction of maximum distance of the speakers mouth from the microphone. y

2. The method of securing a uniform response in a microphone independent, of the position of tioning a microphone having a' directional response adjacent to the speaker with its direction of maximum response in the direction of the speakers mouth when turned away from the microphone, and with a direction of less response in the direction of the speakers mouth when turned most nearly toward the microphone.

. RICHARD W. 'CARIJSLE.

the speakers head, comprising the step of posiv 

